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outboard high-level pilot valve. Fueling continues while the outboard
high-level pilot valve is still open. When the fuel level reaches full,
the outboard high-level pilot valve closes and the resultant back
pressure in the outboard sense line closes the shutoff valve. Fueling
stops.
(6) Partial Load Fueling:
The preferred method for partial load fueling requires Essential DC
bus power in order to use the L and / or R REMOTE FUELING
SHUTOFF switches (cockpit overhead panel) to control fuel flow,
and the standby fuel quantity indicator (copilot’s flight panel) to
monitor fuel quantity. When the desired amount of fuel has been
uploaded into the wing tank(s), the REMOTE FUELING SHUTOFF
switch(es) are selected to CLSD. This supplies 28 VDC to the
respective fuel shutoff solenoid valve. The valve opens and the
resultant back pressure against the pilot valve float system stops
fuel flow to the tank(s).
NOTE:
Before fueling, it is recommended that the aircraft be
positioned with the wings laterally level and with the
nose gear at the low portion of the ramp.
NOTE:
The amber L-R FUEL LEVEL LOW caution Crew
Alerting System (CAS) messages are prompted for
display at approximately 650 lb (295 kg). These
messages may erroneously appear at greater fuel
loads when the boost pumps are not operating. Proper
operation should resume when the boost pumps are
selected on.
B. Defueling System:
The aircraft may be defueled by suction defueling or pumping. If necessary,
after defueling, any remaining pockets of fuel may be removed by wing
draining.
Suction defueling takes place through either the fueling adapter or main
wheel well fuel drains. Suction defueling through the fueling adapter is
OPERATING MANUAL
2A-28-00 PRODUCTION AIRCRAFT SYSTEMS
Page 16
October 11/01
Revision 5
basically the reverse of the fueling process: fuel is drawn from the fuel
tanks through the fueling lines. Suction defueling through the main wheel
well fuel drains requires connecting drain hoses to the drain valves. With
the appropriate equipment, a fuel truck drains the tanks. Neither suction
method will result in completely empty tanks. Approximately 150 gallons
will remain, primarily in the left tank. This can be removed by the pumping
method, if desired.
Defueling by pumping is a method whereby fuel from the wing tanks is
forced through main wheel well fuel drains by the boost pumps. This
method leaves much less fuel remaining than the suction methods,
however, caution is required to ensure the boost pumps are not run dry for
more than three minutes, to prevent pump damage.
Regardless of the defueling method, opening the INTER TANK valve
(cockpit overhead panel) allows fuel to gravity flow from the left hopper to
the right hopper as the right hopper level drops during defueling.
Once defueling is completed, the FUEL LOW LEVEL circuit breaker must
be pulled to prevent damage to the system with power applied to the
aircraft.
C. Fuel Boost Pumps:
(See Figure 3 and Figure 5.)
Two electric motor-driven boost pumps are mounted on the rear spar in
each main wheel well. All four pumps are identical and interchangeable,
but for the purposes of identification, the inboard pumps are designated as
main pumps and the outboard pumps are designated as alternate pumps.
The pumps are capable of operation for as long as fuel is available.
Each pump consists of a fuel-cooled 28 VDC motor that drives a lowpressure
impeller. When operating, each pump supplies fuel at 22 psi
(minimum) at a maximum flow rate of 8,000 PPH. The inlet and discharge
ports of the pumps extend through the rear beam into the pump manifold.
Spring-loaded flapper valves on the manifold’s inlet and discharge ports
close to allow pump removal without defueling the fuel tank. Operating
pressure opens the discharge port flapper valve; installing the pump opens
the inlet port flapper valve.
(1) Fuel Pump Manifold:
The fuel pump manifold, located in the rear of the fuel hopper, is
composed of two suction chambers and a single pressure chamber.
Each suction chamber connects to separate suction line with an inlet
screen. An anti-cavitation float valve in each suction line prevents
pump cavitation by supplying fuel through the valve if an inlet screen
clogs. From the inlet screen, the pump draws fuel from the bottom of
the hopper into the suction chamber, then through the suction port
flapper valve, into the pump. Rotation of the pump impeller
pressurizes the fuel and delivers it at low pressure through a
discharge port flapper valve into the pump manifold pressure
　
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